1. Field of the Invention
The present invention pertains generally to wavelength-selective switches (WSS), and more particularly to a 1×N2 WSS that uses a two-dimensional array of input/output fibers whereby the number of output ports are significantly increased.
2. Description of Related Art
Wavelength-selective switches (WSS) that support individual wavelength switching are of great interest for transparent optical networks. Recent advances in WSS technologies have revolutionized optical fiber communication networks. Wavelength-selective switches have received a great deal of attention because their ability to route different wavelength channels independently. For example, Ford et al. proposed the first MEMS (Micro-Electro-Mechanical Systems)—based optical add/drop multiplexer (OADM) using a digital micromirror array (J. E. Ford, V. A. Aksyuk, D. J. Bishop, and J. A. Walker, “Wavelength add-drop switching using tilting micromirrors,” J. Lightwave Technology, vol. 17, p. 904–11, 1999, incorporated herein by reference). The use of MEMS micromirrors offers lower insertion loss and faster speed than liquid-crystal-based OADM (J. S. Patel and Y. Silberberg, “Liquid crystal and grating-based multiple-wavelength cross-connect switch,” IEEE Photon. Technol. Lett., 7, 514–516 (1995), incorporated herein by reference). This OADM is essentially a 1×1 wavelength-selective switch; however, a multiport wavelength-selective switch can be realized by replacing the digital micromirrors with analog micromirrors and expanding the input/output fibers into a linear array. This is a useful network element because it can be used either as a versatile multiport add-drop multiplexer or as a basic building block for N×N wavelength-selective crossconnect (WSXC).
Several 1×N WSS configurations also have been reported. Examples of such configurations as described in D. M. Marom, et al., “Wavelength-selective 1×4 switch for 128 WDM channels at 50 GHz spacing,” 2002 Optical Fiber Communication (OFC) Conference, Postdeadline Papers (FB7), Anaheim, Calif., Mar. 17–24, 2002, FB7, incorporated herein by reference; A. R. Ranalli, B. A. Scott, J. P. Kondis, “Liquid crystal-based wavelength selectable cross-connect,” ECOC 1999, incorporated herein by reference; T. Ducellier, et al., “The MWS 1×4: a high performance wavelength switching building block,” ECOC 2002, incorporated herein by reference; and S. Huang, J. C. Tsai, D. Hah, H, Toshiyoshi, and M. C. Wu, “Open-loop operation of MEMS WDM routers with analog micromirror array,” 2002 IEEE/LEOS Optical MEMS Conf., incorporated herein by reference.
Such switches are basic building blocks for N×N fully non-blocking wavelength-selective optical crossconnect. In current switch designs, however, the port count is limited by optical diffraction. Note that the switches reported to date are generally limited to 1×4, though adding circulators to each port can double the port count.
For example, FIG. 1 schematically illustrates a WDM router 10 implemented with a one-dimensional (1D) analog scanning micromirror array 12. This router can handle multiple spatial and multiple wavelength channels at the same time. The optical beams 14 from input/output fibers are first collimated and then dispersed by a diffraction grating 16. Each wavelength is focused onto a corresponding micromirror 18 in array 12 by a focusing lens 20. The wavelength can be routed independently to any of the fibers by tilting the corresponding micromirror. As can be seen, however, the maximum number of input/output fibers will be limited by optical diffraction for a given number of wavelength channels.
It will be appreciated that larger port count (≧10) WSS configurations are needed for high capacity networks. The present invention satisfies that need, as well as others, and overcomes limitations in current WSS switch designs.